Edit in Word in Firefox produces a Java Script error in the browser containing the following:
This may happen after you have upgraded into a new Microsoft Office Suite.
The Firefox file extension may be corrupted.
To resolve this problem,
In your Firefox Browser, choose Tools > Add-ons > WebDAV Launcher > Options. This will bring up a pop up window, with a list of office extensions and the file handler. Delete each of them if you are using Microsoft Office.